Pisces’ biggest challenge when trying to identify fisheries with lower environmental impact is lack of research, particularly for inshore fisheries. Following the Bean’s earlier research collaboration on avoiding marine mammal catches, in late 2010 they hosted CEFAS researchers who evaluated the effect of different gill net mesh sizes on catch composition of the red mullet fishery. CEFAS’s research, now published, is both valuable and thought provoking.

Gill nets, used appropriately, are well known for their tendency to select a ‘slot size’ of fish - smaller fish with gills pass through the nets, while larger fish cannot get their heads far enough into the mesh to get trapped. Earlier work with Sussex fisher Graham Doswell, and with Rob Clark of the then Sussex SFC, indicated that unusually large gillnets were catching larger cod, and it is well established that gill nets are size selective for red mullet, for example from Mediterranean research, albeit with much smaller mesh sizes catching much smaller red mullet. This ability to select for certain sizes is potentially a valuable tool for fish stock conservation.

The background to CEFAS’s research is that the size of fish that can be landed (by both ‘mobile gears’ such as trawls and ‘fixed gears’ such gill nets) is dictated by minimum landing sizes and also by a key Council Regulation EC 850/98 ‘for the conservation of fishery resources through ... the protection of juveniles’. For any particular range of mesh sizes, there is one list of fish species deemed by EC 850/98 to be adult, and a second list which are anticipated to be juveniles (i.e. not yet bred). The landed catch must include 70%, by weight, of species on the first list. For Cornwall, for 50-70 mm mesh such as red mullet fixed gear, the species likely to contribute to the 70% are scad, mackerel, and red mullet (positively identified on these trips as Mullus surmuletus). All other species must make up no more than 30% of landings (EC 850/98 Annex VI). Catching more than 30% is legal, providing that discarding keeps the retained percentage below 30%. Having a quota for the species is irrelevant. The idea is to encourage (but does not compel) the development of fishing methods that either don’t catch juvenile fish, or which allows them to be returned to the sea alive and unharmed.

The aim of the research, by Rob Forster and Samantha Smith, was to establish how selective different red mullet gear mesh sizes were. 63mm, 68mm, 75mm and 80mm meshes were used, the last two falling within a normally banned range between 70-90mm, intended to protect salmonids and sea bass. The Beans also had a derogation permitting them to land all fish over the minimum landing size (and allow the fish to be weighed for the research).

Essentially the research indicated 1) that the proportion of fish that would normally have to be discarded was 70% or greater by weight of the total catch, increasing with increasing mesh size 2) that immediate survival rates of discarded fish were very high, in excess of 80%, for cod, pollack, haddock, pout, streaked gurnard, red gurnard and ballan wrasse. Of the fish recorded, only whiting had a low survival rate, of 20%. Presumably high survival was due to the shallow depth at which the nets were set, short soak times, and not being mashed around in a trawl. 3) The total catch reached a plateau after a 2 hour soak time. 4) It was evident that larger meshes caught larger red mullet, pollack, whiting, haddock, bib (pout), mackerel, ballan wrasse, and cuckoo wrasse. Lesser spotted dogfish (no gill covers), red gurnard and streaked gurnard (lots of protuberances to get caught up) indicated no relation between mesh size and size of the fish. Rather surprisingly, cod here also showed no such relationship.

The researchers also touched on the current issue of a new legal requirement for using an Omega Gauge for measuring mesh size, which is more standardised but which stretches the mesh further than before. This means that some gear bought as being under 70mm is now illegal. This will result in an effective shift to smaller mesh sizes and smaller fish caught, which few would regard as a desirable outcome. It also indicates that larger mesh, previously illegal, will now be deemed to be over 90mm. This opens up some tricky issues. Few were aware that there were larger red mullet out there, because the gear that catches them was illegal. Have these fish bred more often, so it does no harm to the stock to catch them? Or do these larger fish create a previously unknown breeding pool, which have sustained the stock, and should be left alone, relaxing concerns about smaller mesh nets? One can throw into the mix Mediterranean research (where red mullet are preferred at a smaller size), where mesh size was between 32-44 mm. Does this mean that the Cornish fishery was already highly sustainable for red mullet? Partly this would be answered by whether a fishery had been sustained over a long time without any change in fishing methods, fishing power or fishing effort, but this sort of data is rare. It is important that we have answers, and that we are more cautious about exploitation rates the poorer the underlying data.

We took several things from this valuable research. First, for this method of fishing, survival rates of fish returned to the sea are good. Second, we have been encouraging short soak times for maximum fish quality and price, something the Beans have taken up with enthusiasm. This work indicates that, for the red mullet fishery, fishers are not loosing out on catch with short two hour soak times. Third, larger meshes generally means bigger fish which is widely assumed to be good (though note the caution above). Last, as the report mentions, this research was seasonally delayed. Gear location and deployment during the normal season may make it easier to avoid whitefish, though we note again the high survival rates of discards recorded in the report.